This study investigated the performance of fluoride adsorption onto a specific tetrametallic oxide adsorbent Fe–Al–Ce-Ni (FACN) and the effect of temperature on adsorption performance. The adsorption performance was determined by adsorption equilibrium, kinetics, and thermodynamic parameters. The adsorption, kinetic, and thermodynamic parameters were compared alternatively. The fluoride adsorption capacity was obtained from four different adsorption isotherm models, namely, Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich (D–R), and Freundlich was found to best fit model. Fluoride removal rate using adsorption (0.27 min–1) was obtained faster than reactive adsorption (0.04 min–1). Several thermodynamic parameters such as enthalpy, Gibbs free energy, entropy (ΔS > 0), and adsorption activation energy were calculated which demonstrated the feasibility and spontaneity (ΔG < 0) and exothermic nature of (ΔH < 0) the fluoride adsorption process. The adsorption process was controlled by a physical mechanism, and the maximum adsorption capacity was found to be 250 mg/g. To our knowledge, this is the first report on the synthesis of tetrametallic oxide adsorbent for fluoride adsorption, and the feasibility of the adsorption process was ratified by three van’t Hoff plots.

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In this study, novel adsorbent ceria nanoparticles (CeNPs) entrapped in tamarind powder (Tm@CeNPs) were efficiently utilized for the simultaneous adsorption of aqueous mercury [Hg(II)] and aqueous lead [Pb(II)]. Surface interactions between the adsorbent and heavy metal ions play an important role in the adsorption process, and the surface morphology can significantly improve the adsorption capacity of the adsorbent. The Langmuir adsorption capacity of Tm@CeNPs for Hg(II) and Pb(II) was found to be 200 and 142.85 mg/g, respectively. The surface area of utilized adsorbent was found to be very high, that is, 412 m2/g. The adsorption kinetics of Tm@CeNPs for both ions follow pseudo-second-order, and the adsorption process is also thermodynamically feasible. Column study favors multilayer adsorption of the heavy metal ion. The spectral analysis of the adsorbent revealed that hydroxyl, carboxylic, and ester groups, as well as CeNPs, are responsible for Hg(II) and Pb(II) adsorption. The cost-benefit analysis confirms the economic viability of the synthesized Tm@CeNPs composite for heavy metal removal. The adsorbent is best suited for Hg(II) adsorption as compared to Pb(II). This is a novel study on the utilization of tamarind leaf powder with CeNPs for heavy metal ion adsorption and its adsorption mechanism, which has not been reported to date.

This research details the synthesis and application of a novel pectin–hydroxyapatite (PHAp) composite for fluoride (F – ) adsorption from aqueous solutions. To determine the efficiency of the adsorption process parameters, i.e., adsorbent dose (0.1–0.4 g), initial fluoride concentration (10–30 mg/L), and temperature (298–313 K), the Box–Behnken design with three levels and three factors have been utilized. The quadratic model was established on 27 batch runs by regression analysis of the experimental data of these runs. The efficacy of adsorption was observed using the Langmuir and Freundlich models. The adsorption rate was found at 3.17 mg g −1 min –1 , and adsorption kinetics followed pseudo-second order (PSO) for PHAp. The significant novelty of this work is the synthesis of unique cubical-shaped rods biopolymer composite from hydroxyapatite. Additionally, this composite showed high adsorption capacity for F – compared to other hydroxyapatite adsorbents, and the improved adsorption capacity is attributed to its unique shape which provides a larger surface area. It can be reused for up to six cycles, which makes this method environment-friendly. The economic viability of the synthesized PHAp composite, in comparison to other adsorbents, is evident from the cost–benefit analysis.

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